In 1998, after workers with Geiger counters detected hot spots in a dumpster full of old cantaloupe rinds, Mr. Johnson sent a technician out to investigate.She homed in on a radioactive speck. “Her meter was going up, and all of a sudden the speck flew away,” Mr. Johnson says. “She called and told me about it, and I said ‘Yeah, right.'”

Mr. Johnson soon learned the specks were radioactive fruit flies. His team traced the flies back to a box with pipes used to transfer waste. It was sealed with a sugar-based coating that contained radioactive material. The flies had noshed on the sealant and flown the radiation to the dumpster.